The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
The present disclosure relates to devices that transmit and measure linear forces along and moments about three orthogonal axes. More particularly, the present disclosure relates to devices that are particularly well suited to measure forces and moments upon a test specimen in a test environment, such as in a wind tunnel.
The measurement of loads, both forces and moments, with accuracy and precision is important to many applications. A common use, where several moments and forces need to be measured, is in the testing of specimens in a wind tunnel. Test specimens can be placed on a platform balance located in a pit of the wind tunnel. The platform balance can be adapted to receive a vehicle or other large test specimen, rather than merely a scale model of the vehicle. Actual vehicles, rather than scale models of the vehicles, allows the designer to determine actual measurements of prototypes, rather than merely inferential measurements. If the test specimen is a vehicle with wheels, the platform balance can be equipped with a rolling belt to rotate the wheels, which can make a significant improvement in measurement accuracy.
Six components of force and moment act on a test specimen on the platform balance in the wind tunnel. These six components are known as lift force, drag force, side force, pitching moment, yawing moment, and rolling moment. The moments and forces that act on the test specimen are usually resolved into three components of force and three components of moment with transducers that are sensitive to the components. Each of the transducers carries sensors, such as strain gages, that are connected in combinations that form Wheatstone bridge circuits. By appropriately connecting the sensors, resulting Wheatstone bridge circuit unbalances can be resolved into readings of the three components of force and three components of moment.
Platform balances have a tendency to be susceptible to various physical properties of the test environment that can lead to inaccurate measurements without additional compensation. For example, temperature transients in the wind tunnel can result in thermal expansion of the platform balance that can adversely affect the transducers. In addition, large test specimens are prone to create large thrust loads on the transducers that can cause inaccurate measurements. Accordingly, there is a continuing need to develop a platform balance suitable for use with large test specimens.